The invention relates to the field of electronic reproduction technology and is directed to a method and to a circuit arrangement for electronic retouching of images, preferably color images.
In electronic color reproduction, three primary color signals (R, G, B) are acquired in a color scanner by pixel-by-pixel and line-by-line, optoelectronic scanning of color originals, these primary color signals representing the color components red, green and blue of the scanned pixels in the color originals. A color correction computer corrects the primary color signals according to the laws of subtractive color mixing into the color separation signals (Y, M, C, K) required for the production of the color separations "yellow", "cyan", "magenta" and "black", which are a measure for the quantities of ink required in the later printing process.
The color separation signals (Y, M, C, K) acquired in the color scanner are digitized and are intermediately stored in a memory for further processing with an electronic image processing system (EIP System). In the image processing system, the digitized color separation values (Y, M, C, K) of individual color originals can be united according to a layout plan to form the data set of an entire page and/or can be subjected to a partial retouch (modifications of chromaticity and/or tone). Partial retouches, i.e., retouches restricted to selectable, limited image regions, are required in order to optimize the corrections that occurred in the color correction computer of the color scanner or, on the other hand, to subsequently undertake editorial changes.
The color separation values (Y, M, C, K) modified in the image processing system are then supplied to a color separation recorder which records rastered or unrastered color separations point-by-point and line-by-line for producing the printing forms for the later printing process.
DE-C-29 20 058 corresponding to U.S. Pat. No. 4,393,399 already discloses a method for partial electronic retouch, whereby digital color values under visual control on a monitor are modified pixel-by-pixel and partially in accordance with the desired retouch effect in the color image or color separation by addition or subtraction of pixel-dependent correction intensity values. For that purpose, the locus coordinates of the pixels to be retouched, or their color values, and the respective degree of retouch are defined by the retoucher, by guiding the coordinate pen of a coordinate acquisition device across the image region to be retouched pixel-by-pixel like a conventional retouch brush. The coordinate pen marks the corresponding pixels and the degree of the retouch for every pixel, for example based on the number of times the pixel is touched with the coordinate pen, from the pressure of the coordinate pen on the pixel or from the dwell time of the coordinate pen on the pixel. In order to be able to more quickly retouch larger image regions, the correction field of the coordinate pen, and thus the number of pixels simultaneously marked can be enlarged, this corresponding to an enlargement of the "brush area" of the "electronic retouch brush."
In the known method, the correction intensity values at the various positions of the coordinate pen are respectively newly calculated into the color values. Such a method, however, more greatly simulates the employment of a stamp than it does the employment of a real retouch brush. A critical difference is comprised therein that an intensity difference that is always the same is calculated into the color values in such a calculation. Given a real retouch brush, however, there is an equilibrium between the retouch ink contained in a reservoir and the respective color application. The respective color output is thus dependent both on the retouch ink in the reservoir as well as on the intensity of the color already present in the color image. When, in the known method, the respective positions for calculating the correction values in are selected lying too far apart, then a chain-like series of brush impressions is produced in the color image to be retouched. When the positions, by contrast, lie too closely together, then a disturbing, chromatic cloud can be formed in the color image to be retouched. When the respective correction value calculations are undertaken in the pixel spacing, then a uniform structure in fact arises in the color image to be retouched, but a work situation that can no longer be simply surveyed with respect to case and effect arises for the retoucher.
It is therefore not adequately possible in the known method to simulate the properties of a real retouch brush. This essentially results therefrom that the operation of the correction intensities was hitherto implemented without taking color balancing events into consideration, as in the case of a real brush retouch.